1. Technical Field
The invention relates generally to grates and grating systems. More particularly, the invention relates to the combination of heavy duty grating subassemblies with lighter duty grating subassemblies such as those used to accommodate both vehicle traffic and pedestrian traffic. Specifically, the invention relates to the combination of a heavy duty grating subassembly formed by welding and a lighter duty grating subassembly formed without welding.
2. Background Information
Within the broad world of grates and grating systems, there is an area which is configured to accommodate vehicle traffic, such as cars and trucks. Such grating involves the use of relatively heavy duty construction. There is also an area of grating to accommodate the walking traffic of pedestrians, and this type of grating involves relatively light weight construction. However, there are locations common to both vehicle and pedestrian traffic and thus there is a need for a grating system which accommodates both groups. The lighter duty construction typically used for pedestrian traffic is not sufficiently strong to support vehicle traffic. On the other hand, the heavy duty grating typically used for vehicle traffic is more costly and weighs a great deal more than the lighter gauge materials.
Typically, the heavy duty grating used for vehicle traffic may use a much greater mesh size than that used for pedestrian traffic. As a result, the spacing between the members of the grating is too great to appropriately accommodate pedestrian traffic. This spacing issue was amplified by the 1990 Americans with Disabilities Act, which required that openings between grating bars be no more than ½ inch in the primary direction of travel, thus better accommodating persons using wheelchairs and walking canes.
One option for resolving this problem is to simply build a grate from the heavy duty materials with a smaller mesh to accommodate pedestrian traffic. This may be achieved, for example, with a grating assembly including bearing bars with cross bars perpendicularly attached thereto by welding or swaging. However, this is very costly and increases the weight of the grating far beyond what is needed in order to accomplish this task. Such a product results in a fairly inefficient strength to weight ratio.
Another possibility is to use filler bars which run parallel to the bearing bars and are disposed between each adjacent pair of bearing bars. Such filler bars may be punched to create notches along one side thereof for receiving the cross bar of the grating. This type of construction presents several problems. First, the filler bars must be installed individually after the bearing bars have been welded to the cross bars. Each filler bar is welded to the cross bar at each intersection to keep the filler bar in place. This is a very time consuming process. In addition, the large number of welds on top of the grating assembly leads to heat induced stresses in the assembly that make it difficult to keep the panel flat. The problems associated with this type of construction limit the widths and spans of grating panels that may be manufactured by this method. Thus, there is a need for a combination of heavy duty grating with relatively light weight grating in order to provide a grating system appropriate for both vehicle and pedestrian traffic.